is he a pure bred? age?

We rescued an adult neutured male from the local animal shelter. He is white/brown, & about 15 inches tall. He has obviously been trained - "sit", "stay", crate trained, housebroke, plays fetch. We are working on getting him to not pull on the leash for walks. He is VERY well behaved. I don't understand why someone wouldn't want this dog! We also have two cats (with claws). The cats quickly let him know who's boss - yet we never leave them alone together!

My question is, how do I determine if he's a pure bred? Is there anyway to get him papered, since we don't know his ancestry? (medical test?)

also, is there a way to accurately find out how old he is?

~beth

ps - I love your site! I went through it before adopting. It was a big help in what to expect!